Method and apparatus for storing plastic preforms in a contaniner

ABSTRACT

In order to store thermoplastic preforms in a container, the outside faces of the preforms are treated so as to make said outside faces more slippery, and the preforms are stored in bulk in the container, with the outside faces of the preforms after treatment presenting a coefficient of friction that is low enough to ensure that the packing density, i.e. the number of preforms stored per unit volume, is greater than the packing density that would be obtained under the same conditions with non-treated preforms.

[0001] The present invention relates to the field of bulk storage ofthermoplastic preforms in a container for handling and transportpurposes.

BACKGROUND OF THE INVENTION

[0002] Receptacles made of polyester, for example bottles made ofpolyethylene terephthalate (PET), are conventionally manufactured in twosuccessive stages: in a first stage, a thermoplastic preform is made byinjecting one or more thermoplastic resins into a mold; in a secondstage, the preform is blown and stretched in a blow mold so as to formthe receptacle. These two stages are not necessarily performedimmediately in line one after the other, and indeed they can beperformed on different production sites. Under such circumstances, it isnecessary to store the preforms on the site where they are produced sothat they can subsequently be taken to the blowing machine which mightpossibly be situated on a different production site that is remote fromthe site where the preforms are produced.

[0003] A first known storage method consists in filling a container withthe preforms in bulk. The container can be made of various materials(metal, card, . . . ), and can have a variety of shapes and sizes. Thepreforms are inserted from above, dropping under gravity into the insideof the open container. In order to reduce the mechanical impacts towhich the preforms are subjected on being introduced into the container,special equipments have been developed so as to cause the height throughwhich the preforms fall to be matched automatically relative tothe-height of the pile of preforms that is building up inside thecontainer, so as to limit the height of fall.

[0004] The major drawback of that method of bulk storage lies in pooruse of the storage volume of the container, which amounts to low packingdensity, i.e. a small number of preforms being stored per unit volume.In practice, it is also observed that a convex dome forms at the topportion of the pile of preforms, where such a dome is characteristic ofpoor utilization of storage volume. However, for manifest economicreasons, associated mainly with the cost of transporting preforms, it isnaturally preferable for storage volumes to be as small as possible,particularly for the purpose of making it possible to transport as largeas possible a number of preforms in a given number of containers.

[0005] In order to improve the packing density of preforms in acontainer, proposals have already been made in the past to storepreforms in ordered manner, by stacking preforms so that they areoriented in such a manner that the preforms in a given row point in theopposite direction to the preforms in an adjacent row. That solution isdescribed in particular in United States patent U.S. Pat. No. 5,555,706.That solution does indeed enable the volume occupied by the preformsinside the container to be optimized in comparison with bulk storage.However, it presents the drawback of requiring special equipment that iscomplex and expensive in order to store the preforms in the container.

OBJECTS AND SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide a novel solutionfor storing preforms in a container which enables packing density (i.e.the number of preforms per unit volume) to be increased compared withthe known method of bulk storage, but which is simpler to implement thanthe storage method described in above-cited patent U.S. Pat. No.5,555,706.

[0007] This object is achieved by the method of the invention forstoring preforms in a container. In a manner that is essential to theinvention, the outside faces of the preforms are treated so as to makesaid outside faces more slippery, and the preforms are stored in bulk inthe container, with the outside faces of the preforms after treatmentpresenting a coefficient of friction that is low enough to ensure thatthe packing density, i.e. the number of preforms stored per unit volume,is greater than the packing density that would be obtained under thesame conditions with non-treated preforms.

[0008] The invention also provides: a method of manufacturing andstoring thermoplastic preforms; apparatus for storing thermoplasticpreforms; and an installation for manufacturing and storingthermoplastic preforms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Other characteristics and advantages of the invention appear moreclearly on reading the following description of two preferredimplementations of the invention, which description is given by way ofnon-limiting example and with reference to the accompanying drawings, inwhich:

[0010]FIG. 1 is an overall view of a first preferred embodiment of aninstallation for manufacturing and storing thermoplastic preforms inaccordance with the invention;

[0011]FIG. 2 is a front view of the treatment receptacle and of thespray nozzle of the storage apparatus of the FIG. 1 installation;

[0012]FIG. 3 shows a thermoplastic preform as provided by the injectionmachine of the FIG. 1 installation; and

[0013]FIG. 4 is a diagram showing a second preferred embodiment of aninstallation for manufacturing and storing thermoplastic preforms inaccordance with the invention.

MORE DETAILED DESCRIPTION

[0014]FIG. 1 shows a preferred embodiment of an installation formanufacturing polyester, e.g. PET, preforms and storing them in acontainer (C), the preforms being of the same type as the preform (P)shown in FIG. 3. In conventional manner, the preforms which aremanufactured and stored in line in the container (C) are subsequentlytaken to a blowing machine enabling thermoplastic bottles to bemanufactured in conventional manner by stretching and blowing thepreforms in a blow mold. When the blowing machine is situated on anindustrial site that is remote from that where the preforms are made,the containers (C) containing the preforms are transported by anyconventional transport means, for example they are loaded onto trucks soas to be taken by road.

[0015] With reference to FIG. 3, a preform (P) is conventionallygenerally tubular in shape having a central axis 1 a, being closed at afirst end 1 b and open at its opposite end 1 c. A preform also has acollar 1 d which enables it to be held in position in the blow mold. Inthe particular example shown, in the portion of the preform that issituated above the collar 1 d and that subsequently forms the neck ofthe bottle, there is provided a screw thread 1 e that subsequentlyserves to receive a screw cap for closing the bottle that is made fromthe preform. In another variant, the preform need not have a screwthread, for example its neck could be shaped in the vicinity of its freeedge so as to enable a capsule to be force-fitted thereon.

[0016] With reference to FIG. 1, the installation for manufacturing andstoring preforms comprises a machine 2 for injecting thermoplasticpreforms which is disposed in line with a storage apparatus 3constituting a preferred embodiment and described in detail below.

[0017] The injection machine 2 is conventional and is therefore notdescribed in detail in the present description. In the usual way it hasan n cavity mold serving to make a batch of n thermoplastic preforms inparallel during each injection cycle. Depending on circumstances, thenumber n of cavities will be greater or smaller, given that the largerthe number of cavities the greater the rate at which preforms areproduced.

[0018] The storage apparatus 3 comprises a conveyor 4 whose upstream endportion 4 a is located at the outlet from the injection machine 2, thusserving to receive batches of n preforms as ejected in succession fromthe machine 2 at the end of each injection cycle after the mold has beenopened. The conveyor 4 serves to take each batch of n preforms insuccession to equipment 5 that performs two functions: the firstfunction is to spray a lubricant onto each batch of n preforms; thesecond function is to enable each batch of n lubricated preforms to beintroduced under gravity by dropping freely into the container (C), withthe height through which the preforms fall being adjustable. For thispurpose, the equipment 5 has a treatment receptacle 6 beneath which thecontainer (C) is placed, and means for spraying a lubricant onto a batchof preforms held temporarily in the treatment receptacle 6.

[0019] More particularly, the treatment receptacle 6 is upwardly open,and it presents a bottom that is retractable so as to allow the preformsto drop, and its vertical position can be adjusted (so as to adjust theheight H through which the preforms fall). In the particular exampleshown, this treatment receptacle comprises two jaws 6 a and 6 b, with atleast one of the jaws 6 b being mounted to pivot about a substantiallyhorizontal axis 7 and being fitted with an actuator 8 enabling it to bepivoted between a first position (drawn in continuous lines in FIG. 1)in which it co-operates with the other jaw 6 a to form a receptaclehaving a closed bottom, and a retracted position (shown in dashed linesin FIG. 1) in which it co-operates with the other jaw 6 a to form areceptacle 6 having an open bottom. In another variant, both jaws 6 aand 6 b could be pivotally mounted in order to open the bottom of thereceptacle 6.

[0020] The downstream end 4 b of the conveyor 4 is positioned verticallyabove the treatment receptacle 6 so that the preforms that are taken bythe conveyor 4 from the outlet of the injection machine 2 drop undergravity from the conveyor 4 when they reach the downstream end 4 b ofthe conveyor and fall into the inside of the treatment receptacle 6.

[0021] The means for spraying a lubricant on the batch of n preformsthat is contained temporarily in the treatment receptacle 6 comprise aspray head 9 (FIG. 2) having two spray nozzles 9 a and 9 b and mountedabove the treatment receptacle 6. In another variant, the spray head 9could have only one spray nozzle, or on the contrary it could have morethan two spray nozzles. In the example shown, the spray head 9 ispivotally mounted about an axis 10 that is substantially horizontal, andit is positioned substantially vertically over the middle of thetreatment receptacle 6. The head 9 is fitted with an actuator 11enabling it to pivot about its axis 10, and the actuator is controlledso as to cause the spray head 9 and consequently the two spray nozzles 9a and 9 b to rock back and forth through a limited angle (A) between twoextreme positions represented respectively by continuous lines anddashes lines in FIG. 2. The angle (A) through which the spray head 9rocks is adjusted so as to enable the spray jets from the nozzles 9 aand 9 b to sweep over the entire bottom of the receptacle.

[0022] The spray nozzles 9 a and 9 b are fed in parallel with a liquidlubricant under pressure, by means of respective feed hoses 12 a and 12b which are connected to a tank of liquid lubricant (not shown) via apump (not shown). The actuators 8 and 11 and the pump for feeding thespray head 9 are controlled by means of a programmable industrialcontroller (not shown) so as to operate synchronously with the cycletime of the injection machine 2 so as to perform the operationsdescribed below.

[0023] The method of the invention as implemented by means of theinstallation shown in FIG. 1 takes place as an iterative cyclecomprising successive operations (a) to (c) described below, each cyclecorresponding to in-line manufacture and storage of one batch of npreforms. Throughout the duration of the method, the conveyor 4 runscontinuously, its belt being driven at a predetermined linear speed thatis substantially constant. Prior to beginning the first cycle, an emptyopen container (C) is positioned beneath the treatment receptacle 6.

[0024] (a) Manufacture and Transport of a Batch of n Preforms

[0025] The injection machine 2 makes a batch of n preforms in anoperating cycle specific thereto. The n preforms are received on theconveyor 4 on leaving the injection machine 2 after its mold has beenopened. The n preforms are conveyed in bulk by the conveyor 4 at apredetermined speed until they come vertically above the treatmentreceptacle 6, into which they drop under gravity. At this stage, thebottom of the receptacle 6 is closed, with the jaw 6 b being in itsposition drawn in continuous lines in FIG. 1.

[0026] b) Processing (Lubricating) a Batch of n Preforms

[0027] The actuator 11 is controlled automatically so as to cause thespray head 9 to rock back and forth as described above, andsimultaneously the two spray nozzles 9 a and 9 b are fed under pressurewith pressurized liquid lubricant. Liquid lubricant is thus sprayed overthe batch of n preforms that are contained in bulk in the receptacle 6.The amount of liquid lubricant sprayed can be adjusted and depends onthe delivery rate of the spray pump and the length of time spraying ispreformed, and the spray nozzle can preform a greater or smaller numberof back-and-forth strokes between its two extreme positions depending oncircumstances. The spray cycle can be triggered periodically as afunction of the duration of the cycle time of the injection machine 2,and/or it can be conditioned by a sensor detecting the presence ofpreforms in the bottom of the treatment receptacle 6.

[0028] c) Dropping the Batch of n Treated Preforms into the Container(C)

[0029] Once the spraying step (b) has been completed, the actuator 8 isautomatically operated to retract the jaw 6 b into its position that isdrawn in dashed lines in FIG. 1 (thereby opening the bottom of thetreatment receptacle 6). The batch of n preforms contained in thereceptacle is thus removed under gravity immediately after beingsubjected to the spray treatment, and the preforms drop into the opencontainer (C).

[0030] The cycle constituted by steps (a), (b), and (c) as describedabove is repeated automatically until the container has been filled witha predetermined number of preforms.

[0031] While they are being stored in the open container (C), thepreforms accumulate in the form of a pile of preforms dropped in bulk.Because they have been sprayed with lubricant, the preforms are mademore slippery relative to one another (i.e. their outside faces presenta lower coefficient of friction). It is thus found in practice thatpreforms within the bulk pile have a natural tendency to positionthemselves and to orient themselves by sliding one over another so as tooccupy as little volume as possible. This improves packing density (thenumber of preforms per unit volume). In practice, this means that thetop surface of the pile of preforms in bulk tends automatically to levelitself, unlike a pile of preforms in bulk when the preforms have notbeen treated, where the surface of such a pile is characterized byforming a convex dome.

[0032] In a particular embodiment, given by way of indication withoutlimiting the invention, the manufacturing and storage method describedabove with reference to FIGS. 1 to 3 has been implemented by sprayingonto the preforms a lubricant constituted by a food grade silicone oilin the liquid state, with spraying taking place at a temperature ofabout 20° C. More particularly, the silicone oil was an oil sold by thesupplier Rhodia Chimie under the trade name Silbione® Oil 70047 V350,which presents at 25° C. a viscosity of 350 (±5%) and a surface tensionat 25° C. of approximately 21.1 nN/m. The preforms were injected usingPET, having an outside diameter d (FIG. 3) of 28 millimeters (mm) and alength l of 150 mm. They were manufactured. in successive batches of 48preforms. Each batch of 48 preforms had about 0.27 grams (g) of siliconeoil sprayed onto it in the receptacle. The container used was octagonalin section having eight sides of respective lengths 300 mm, 740 mm, 300mm, 550 mm, 300 mm, 750 mm, 300 mm, and 550 mm and a height of 1 meter(m), and it was filled to the top with 6700 preforms. Filling level wasmonitored by visually inspecting the height of the fill.

[0033] By way of comparison, an identical container was filled with PETpreforms that were not treated with lubricant and under the same storageconditions, i.e. using the FIG. 1 installation with the preformsdropping through the same height and without using the spray nozzle tospray any lubricant. The container was filled with it contained 5800preforms. The container was deemed to be filled when the top of theconvex dome surface of the pile of preforms reached the filling level ofthe container. The packing density of treated preforms was consequentlyapproximately 16% better than that obtained under the same conditionsbut using non-treated preforms.

[0034] The invention is not limited to implementing the particularsilicone oil mentioned above, but it extends more generally to anytreatment for lubricating all or at least some of the outside faces ofthe preforms in order to obtain a coefficient of friction for saidoutside faces that is low enough to increase the number of preforms thatcan be stored in bulk in a given volume. The lubricant is preferablyselected and applied to the preforms in such a manner that the packingdensity of the preforms is at least 10% and preferably at least 15%greater than the packing density that would otherwise have been obtainedunder the same conditions but using untreated preforms.

[0035] Amongst the lubricants that are suitable for being used,particular mention can be made in non-exhaustive manner of vegetableoils having an emulsifying agent of the E322 type as are commonly usedin the food industry, or indeed a mixture of vegetable oil and waxincorporating an emulsifying agent (E322) and at least one antioxidizingagent (E306).

[0036] The lubricant is not necessarily applied by spraying, and thelubricant could, in a variant, be applied by immersing the preforms in abath of lubricant or by coating the preforms in the lubricant.

[0037] Similarly, the treatment with lubricant need not be performed ona batch of preforms, but could be performed individually on eachpreform, for example by means of an installation as shown in FIG. 4.This installation comprises a unit 13 for manufacturing preforms byinjection molding (an injection machine implementing a mold having oneor more cavities in conventional manner), which machine is fitted at itsoutlet with an apparatus 3′ enabling lubricant to be applied to thepreforms and enabling the lubricated preforms to be stored in acontainer C. The apparatus 3′ includes a conveyor 14 for taking preformsas manufactured by the unit 13 in bulk from its outlet and bringing themto a machine 15 for storing preforms of the kind commonly referred to asan “unscrambler”. This machine 15 is known to the person skilled in theart and comprises a screen (or receptacle) in which the preforms areintroduced in bulk under gravity, and it delivers the preforms one byone, with each preform being oriented in a predetermined position(collar up in the example of FIG. 4). At the outlet from the machine 15,the preforms P are taken individually and in line in the transportdirection represented by arrow D by means of a conventional transfersystem 16 for taking the preforms P individually to the storagecontainer C while ensuring that each preform remains in the sameorientation. The transfer system 16 contains one or more spray nozzles18 fed with lubricant such as silicone oil, for example. The nozzle 18is positioned on the path of the preforms P beneath the level of thecollar 1 d of the preforms P. In operation, each preform P is taken bythe transfer system 16 and passes in front of the spray nozzle 18 whileoriented in the position shown in FIG. 4. The spray nozzle 18 sprays ajet towards each successive preform, enabling the outside surface of thebody of the preform P to be lubricated, but only in its portion thatextends beneath the collar 1 d of the preform P. The spray jet can becontinuous or on the contrary it can be triggered by a sensor detectingthe presence of a preform to be lubricated. After lubrication, eachpreform is removed automatically under gravity from the transfer system16 and drops into the container C. The main advantage of the variantshown in FIG. 4 is that it makes it possible to ensure that lubricantdoes not penetrate into the insides of the preforms.

[0038] In order to further increases the packing density of lubricatedpreforms contained in the container (C) in the variants of FIG. 1 or 4,it is also advantageously possible to subject the container (C) tomechanical shaking, by causing it to vibrate and/or oscillate, therebyminimizing the volume occupied by the preforms inside the container.This can be done using a vibrating and/or oscillating platform on whichthe container (C) is placed. An example of a vibratory apparatus that issuitable for use is described in particular in international patentapplication WO-A-95/18043.

1. A method of storing thermoplastic preforms in a container, whereinthe outside faces of the preforms are treated so as to make said outsidefaces more slippery, and the preforms are stored in bulk in thecontainer, with the outside faces of the preforms after treatmentpresenting a coefficient of friction that is low enough to ensure thatthe packing density, i.e. the number of preforms stored per unit volume,is greater than the packing density that would be obtained under thesame conditions with non-treated preforms.
 2. A method according toclaim 1, wherein the outside faces of the preforms after treatmentpresent a coefficient of friction that is low enough for the packingdensity, i.e. the number of preforms stored per unit volume, to be atleast 10% and preferably at least 15% greater than the packing densitythat would be obtained under the same conditions with untreatedpreforms.
 3. A method according to claim 1, wherein the step of treatingthe preforms consists in applying a lubricant over all or part of theoutside surfaces of the preforms.
 4. A method according to claim 2,wherein the lubricant is selected from the group: silicone oil;vegetable oil incorporating at least one emulsifying agent; and amixture of vegetable oil and wax incorporating at least one emulsifyingagent and at least one antioxidizing agent.
 5. A method according toclaim 4, wherein the lubricant is applied in liquid form.
 6. A methodaccording to claim 3, wherein the method of applying the lubricant isselected from the group: spraying, coating, immersing.
 7. A methodaccording to claim 6, wherein the preforms are treated in successivebatches of n preforms in bulk, and by spraying a lubricant onto eachsuccessive batch of n preforms in bulk.
 8. A method according to claim7, wherein each successive batch of n preforms is conveyed in bulk bymeans of a conveyor to a treatment receptacle positioned above thecontainer for storing the preforms, wherein each new batch of preformsin bulk contained in the intermediate receptacle is subjected to alubricant being sprayed onto the preforms in bulk of said batch, and atthe end of spraying the bottom of the receptacle is opened so that thebatch of preforms drops under gravity into the container.
 9. A methodaccording to claim 3, wherein each preform is conveyed individually tothe container with each preform being maintained in a given orientation,and wherein prior to each preform being introduced into the containerlubricant is applied to the oriented preform solely on that portion ofthe preform which extends beneath the collar of the preform.
 10. Amethod according to claim 1, wherein the preforms are introduced intothe container immediately after the treatment step.
 11. A methodaccording to claim 1, wherein the container is caused to vibrate and/oroscillate in such a manner as to reduce the volume occupied by thepreforms stored in the container.
 12. A method of manufacturing andstoring thermoplastic preforms, wherein injected thermoplastic preformsare manufactured in series, and wherein as preform manufactureprogresses, the preforms are stored in line in a container using themethod of claim
 1. 13. Apparatus for storing thermoplastic preforms in acontainer, the apparatus comprising a receptacle for treating preforms,which receptacle is open on top, and has a bottom that is retractable atleast in part on command, a conveyor having a downstream end positionedabove the treatment receptacle, and serving to convey one or morepreforms automatically to the treatment receptacle, and at least onespray nozzle for spraying a lubricant mounted over the treatmentreceptacle.
 14. Apparatus according to claim 13, wherein the spraynozzle is fed with a lubricant selected from the group: silicone oil;vegetable oil incorporating at least one emulsifying agent; and amixture of vegetable oil and wax incorporating at least one emulsifyingagent and at least one antioxidizing agent.
 15. Apparatus according toclaim 14, wherein each spray nozzle is designed to be driven withreciprocating pivoting motion about a substantially horizontal axisthrough a limited angle.
 16. Apparatus for storing thermoplasticpreforms in a container, the apparatus comprising a machine for storingpreforms, which machine is designed to be fed with preforms in bulk andto deliver preforms one after another in such a manner that each preformis in a predetermined orientation, a transfer system enabling preformsto be taken from the outlet of the unscrambler, and to take themindividually to the container while maintaining the orientation of eachpreform, and means for spraying a lubricant, which means are positionedon the path of the preforms so as to enable the lubricant to be appliedto each oriented preform only on the portion of the preform that extendsbeneath the collar of the preform.
 17. Apparatus according to claim 16,wherein the spray means are fed with a lubricant selected from thegroup: silicone oil; vegetable oil incorporating at least oneemulsifying agent; and a mixture of vegetable oil and wax incorporatingat least one emulsifying agent and at least one antioxidizing agent. 18.An installation for manufacturing and storing thermoplastic preforms ina container, the installation comprising an injection machine forinjecting thermoplastic preforms and fitted at its outlet with a storageappliance according to claim 13.